84841

Appears in sequences

• Number of intersections of diagonals in the interior of a regular n-gon.at n=41A006561
• Indices k such that 3 plus the k-th triangular number is a perfect square.at n=12A154138
• Semiprimes formed by concatenating n, n, and 1 for n = 1, 2, 3,....at n=35A210711
• a(n) = n! * Sum_{k=0..floor(n/3)} (n - 3*k)^k/(6^k * (n - 3*k)!).at n=10A356328